In the processing and packaging of semiconductor devices, wire bonding continues to be the primary method of providing electrical interconnection between two locations within a package (e.g., between a die pad of a semiconductor die and a lead of a leadframe). More specifically, using a wire bonder (also known as a wire bonding machine) wire loops are formed between respective locations to be electrically interconnected. The primary methods of forming wire loops are ball bonding and wedge bonding. In forming the bonds between (a) the ends of the wire loop and (b) the bond site (e.g., a die pad, a lead, etc.) varying types of bonding energy may be used, including, for example, ultrasonic energy, thermosonic energy, thermocompressive energy, amongst others. Wire bonding machines (e.g., including stud bumping machines) are also used to form conductive bumps from portions of wire.
During ball bonding operations, a tail of wire extending from the tip of a bonding tool (e.g., a capillary) is melted into a free air ball using a spark from an electronic flame-off (EFO) device. The free air ball is then used to form a first bond (e.g., a ball bond) of a wire loop at a first bonding location, and then wire is extended from the ball bond to a second bonding location, where a second bond (e.g., a stitch bond) of the wire loop is formed by bonding a portion of the wire to the second bonding location using the bonding tool. For example, the first bonding location may be a bonding pad of a semiconductor chip, and the second bonding location may be a lead of a leadframe. The bonding tool may then be raised to a short tail detect height where the wire is tested (e.g., an electrical continuity test) to ensure it is still continuous with the stitch bond on the second bonding location. If a short tail is not detected, the bond head (i.e., carrying the bonding tool and a wire clamp, now closed) is raised to tear the wire at the stitch bond. The remaining tail length may then be used to form another free air ball for another wire loop.
Referring specifically to FIG. 1A, selected elements of wire bonding machine 100 are illustrated. Wire bonding machine 100 includes support structure 102 (e.g., a heat block, an anvil, etc.) that supports substrate 104. Substrate 104 includes contact portion 104a (which may be referred to herein as bonding location 104a). In a specific example, substrate 104 is a leadframe, and contact portion 104a may be a lead 104a of leadframe 104. Semiconductor die 106 is supported by substrate 104. Wire bonding machine 100 also includes bonding tool 110, wire clamp 112 (in an open position in FIG. 1A), wire 114, and detection system 116. Wire 114 is provided by a wire supply (e.g., a wire spool on wire bonding machine 100, not shown). Bonding tool 110 (e.g., a capillary) is used to form wire loop 108 between semiconductor die 106 and substrate 104. More specifically, first bond 108a of wire loop 108 has been bonded to a bonding location of semiconductor die 106. Likewise, second bond 108b of wire loop 108 has been bonded to a bonding location of contact portion 104a of substrate 104. In FIG. 1A, bonding tool is shown at a second bond formation height h0.
After formation of wire loop 108, it is now time to form a wire tail for a subsequent wire loop. Referring now to FIG. 1B, bonding tool 110 has been raised (e.g., along with wire clamp 112 and other elements of a z-axis motion system of bonding machine 100, not shown) to a height h1 (which may be referred to as “tail height” 118) such that wire tail 114a extends below bonding tool 110. At this time wire clamp 112 is closed, and detection system 116 is used to perform a continuity check. That is, as is known to those skilled in the art, detection system 116 senses electrical continuity in a circuit that includes wire clamp 112, wire tail 114a, second bond 108b, etc. That is, if wire tail 114a is still continuous with second bond 108b at h1 (as shown in FIG. 1B), then electrical continuity is sensed and there is no short tail condition. Conversely, if wire tail 114a is not continuous with second bond 108b at h1, then no electrical continuity is sensed and there is a short tail condition. Detection system 116 may be referred to as a bond integrity test system (i.e., a BITS system) on certain wire bonding machines.
Short tail conditions may result in a number of problems during wire bonding such as, for example, inconsistent free air ball size and shape. Thus, it would be desirable to provide improved short tail recovery techniques during wire bonding operations.